1. Field of the Invention
The present invention relates to brake systems for releasably locking parallelogram linkage support arms for supporting dental trays in a dental operatory. In particular, the present invention is directed to an air brake assembly to provide the aforementioned locking function.
2. State of the Art
Parallelogram linkages for supporting a dental tray horizontally at a multitude of vertical positions are conventional and old in the art. See for example U.S. Pat. Nos. Re. 8,723 and 171,746 issued to E. T. Starr, U.S. Pat. No. 466,464, issued to J. Hood et al and U.S. Pat. No. 1,050,672, issued to J. H. B. Macintosh. The Starr patents employ a ratchet mechanism and the Hood et al patent utilizes similar teeth-like projections and an engaging rod to prevent relative movement of the parallelogram linkage arms. More recently, U.S. Pat. No. 3,160,379, issued to J. M. Gardella describes a pawl mechanism for locking the parallelogram linkage members. Likewise, U.S. Pat. No. 3,237,902, issued to K. Hayashi utilizes a pawl mechanism for preventing pivotable movement of the parallelogram linkage members. In U.S. Pat. No. 4,082,244, issued to L. K. Groff, a threaded member is used to fix the relative position of the linkage arms of the parallelogram to prevent their movement.
While such systems can provide a useful function, they have not been found entirely satisfactory. Pawl and ratchet mechanisms operate in discrete increments and the transition of the support tray between different positions does not always take place smoothly. Unless such transition is smooth, instruments placed on the tray can be displaced or fall from the tray to areas where they may become contaminated and thus require cleaning before reuse. Additionally, actuation of such mechanisms which typically are enclosed in the support arm housing from remote locations is not conveniently provided for. Typically, two handed operation by the dental practioner is required. It usually is necessary for the dental practioner to hold the tray at the adjusted position with one hand while at the same time attempting to release or lock the particular locking mechanism provided in prior art devices. For example, as with the Groff mechanism, it is apparent that it is no easy task to hold a dental tray at a particular position while at the same time rotating the threaded locking mechanism which is provided in the support arm at a location remote from the dental tray. The actuating button of the Gardella device also is provided in the link arm. It is necessary then to support the dental tray with one hand while at the same time depressing the actuating button with the other hand to move the linkage arm to the desired position. The Hayashi device utilizes a remote actuation system with a relatively complex lever and rod mechanism to operate the pawl system.
Thus it is seen that there is a need for a simple locking and brake mechanism for parallelogram linkage arms for use with dental support trays which can be conveniently actuated from a remote location, particularly from a location on the dental tray itself. Additionally, since dentists and dental assistants work for many hours from trays supported near the patients, small variations in tray positions can greatly increase the fatigue factor involved in such work. Accordingly, it is desirable to have a tray support which is positionable at substantially an infinite number of positions, rather than at a few discrete position.